The present invention relates to a method and apparatus for cutting sheet material by means of a cutting blade such as a reciprocating blade. More particularly, the present invention resides in an automatically controlled cutting machine that can be optionally programmed at the machine or operator's discretion to cause special cutting techniques to be utilized by the blade during the cutting operation. The optional programs are selected based on knowledge, testing and prior experience and take into consideration such factors as the type of sheet material being cut, the special features or contours of the patterns or array of patterns being cut, the proximity of adjacent lines of cut, the depth of the sheet material and the desired accuracy of the finished product.
The techniques of controlling the motions of a cutting blade as it advances along a cutting path through a layup of sheet material are based partly on technical reasoning and partly on experience in the art. For example, in U.S. Pat. Nos. 3,855,887 and 3,864,997 issued to Pearl and Robison and having the same assignee as the present invention, a yawing technique is disclosed and claimed for controlling a reciprocating cutting blade as it advances along a cutting path in close proximity to adjacent cuts. Such technique comprises rotating the cutting blade slightly out of a position tangent to the cutting path and away from a previous adjacent cut to prevent the cutting blade from jumping into the previous cut as a point of tangency is approached.
The special techniques for controlling motions of a cutting blade cause the blade to track a desired cutting path with minimal error in spite of the complex loading of the blade which affects its cutting operation, particularly in multi-ply layups of sheet material. Stress and strain within the blade cause the blade to deviate from a desired cutting path in spite of the accuracy with which servomechanisms or other positioning mechanisms locate the blade, and without the special techniques, the deviations are often sufficient to produce cutting errors which are too significant to be ignored.
Several objects are achieved by the special techniques of controlling blade motions. First of all, it is highly desirable to have uniformity among pattern pieces which are cut at different positions in a multi-ply layup of sheet material. Such uniformity enables pattern pieces to be interchanged and assembled in a finished product such as an item of upholstery or a garment with greater ease and consistent quality.
Secondly, with greater assurance that the cutting blade will track a desired cutting path, pattern pieces may be more closely packed in the marker or array of pattern pieces cut from a piece of sheet material. Closer packing conserves material and since the material is a significant factor in the cost of a finished product, the product can be manufactured at a lower cost.
It has been found from experience that the special cutting techniques are not always needed. Some sheet materials or markers can be cut quite satisfactorily without adapting the machine to use special techniques and, in fact, if the techniques are employed, the resulting pattern pieces may be less accurate because of different material behaviors and cutting conditions. On the other hand, the special techniques may be employed advantageously in other situations and, it is desirable to have the option of employing the techniques.
In the prior art Pat. Nos. 3,855,887 and 3,864,997 referenced above, the special cutting techniques are integrated into the cutting program at the digitizing stage. Therefore, it was not possible for the operator or the cutting machine to be selective in the employment of the techniques after the contours were set in the digitized data.
Furthermore, the special cutting techniques disclosed in the referenced patent were employed only in limited circumstances. It has been determined, however, that a more general application of special techniques is needed if discretion to use the techniques is to be allowed. Accordingly, new techniques have been conceived which have broader application, and it is these techniques that form the basis of the optional programs of the present invention.
Accordingly, it is a general object of the present invention to provide method and apparatus for cutting sheet material by introducing special cutting techniques into a cutting operation when needed or desired. It is a further object of the invention to disclose new cutting techniques which are suitable for general application to the cutting of pattern pieces, especially when the techniques are offered as optional cutting programs.